LOS ANGELES – Forty years later, Peter Fonda cracks up explaining why a grinning, glassy-eyed Jack Nicholson did an awesome job of acting high on pot in an infamous “Easy Rider” campfire scene. Simply put, that was no acting. And co-stars Fonda and Dennis Hopper also smoked real grass on-screen during their rambling campfire chats.

Nicholson, who earned his first Oscar nomination for the 1969 cult classic, plays a boozing ACLU lawyer who in the campfire scene is being introduced to marijuana by bikers Billy (Hopper) and Wyatt (Fonda). Things may have gotten convoluted because Hopper, who was also the film's director, decided to shoot his and Fonda's parts first while Nicholson sat nearby, off-camera.

“We would do our lines and I would fire up a joint and pass it to Jack, and Jack would take a hit on it,” recalls Fonda, who not only acted but also co-wrote and produced the film. “By the time we get to him, he's stoned out of his brain. In a stoner way, as we're filming, he forgot his lines – it was a long speech about (Venusians) meeting people from all walks of life.”

Nicholson's giggle-punctuated babble about UFOs fits perfectly in “Easy Rider,” the counterculture film that helped propel him to stardom. (It returns, in a newly restored 35mm print, for an exclusive engagement beginning tonight at the Ken Cinema.) Fonda and Hopper received Oscar nods for the screenplay co-written with Terry Southern. (Much of the dialogue was improvised, however.)

Premiering July 14, 1969, the road-trip flick stars Fonda and Hopper as two disillusioned, shaggy-haired bikers who encounter prejudice and bigotry as they ride cross-country during the turbulent '60s. The low-budget box-office hit was groundbreaking; it reflected the social and political climate and was shot in less than seven weeks with $500,000 of nonstudio money, ushering in the wave of indie filmmaking.

What went on behind the lens, though, adds even more to the “Easy Rider” lore. The talkative 69-year-old Fonda, who conceived the movie's idea and plays the cool Wyatt, aka Captain America, in a recent interview discussed it all – from Hopper's maniacal rants to the time Nicholson nervously squeezed so hard with his legs while holding on the back of Fonda's chopper, he cracked Fonda's rib.

The way Fonda tells it, the whole production was unconventional. Just listen to how he got his iconic American flag-emblazoned leather jacket and tight leather pants to look worn: “I stood in my shower and got it soaking wet. And then I sat in the sun with my legs bent and my arms bent and let it dry.”

But the Hollywood scion – his father is the late Henry Fonda – turns serious when he recounts the powerfully emotional scene in which he clings to a female statue in a New Orleans cemetery while on a bad acid trip. In the film he calls the statue “Mother,” asks why she left and sobs, “I hate you so much.”

Before cameras rolled, Hopper had asked Fonda to talk in the graveyard about his mother, Frances. She committed suicide when Fonda was 10 and his actress sister Jane was 12.

“I didn't want to do it. Dennis and I were arguing about it and finally Dennis, with tears in his eyes, he's begging me to do it. I said, 'Well, give me one good reason.' He said, 'Because I'm the director.' I couldn't argue with it.

“I had never gone there before about my mother. I had never gone down that road. It was very upsetting to me.”

Fonda says the scene later helped persuade Bob Dylan to allow use of “It's Alright, Ma (I'm Only Bleeding)” on the “Easy Rider” soundtrack. Dylan had originally balked, according to Fonda, because he didn't like his harmonica-playing on the song, the lyrics of which include, “Suicide remarks are torn / From the fool's gold mouthpiece.”

“I said, 'I've got to hear those words, because my mother cut her throat from ear to ear in an insane asylum when I was 10.' And that blew his mind. Bobby looked at me and said, 'OK.' ”

From the get-go, filming started off shakily, according to Fonda. The first sequence shot was in New Orleans, and the voice of Hopper on-screen is raspy for good reason. Over the years, “Easy Rider” cast and crew members have recounted how a controlling Hopper went ballistic at times. Fonda, who describes Hopper as both “brilliant” and “paranoid” (he had his own burly bodyguard during filming), says the director was definitely the latter when he gathered the ad hoc crew on the first day in a parking lot.

“Dennis was screaming at us. It's his 'effing' movie and nobody was going to take his 'effing' movie away from him. He was literally screaming the same thing over and over for an hour, and he lost his voice.”

By the time Hopper was done yelling, the Mardi Gras parade, which was to figure prominently in the movie, had already kicked off. That was a huge screw-up, since the filming permit stated the actors had to start with the parade at the beginning. At one point, a cameraman sneaked in and shot actress Karen Black briefly jumping into the parade.

If the production's start was dicey, so was the end. Fonda's and Hopper's customized Harleys (which were former Los Angeles Police Department bikes bought at auction for $500 apiece, then “built by five black guys from Watts,” according to Fonda) aren't in the final campfire scene.

“We had already had a wrap party. We had forgotten to shoot that scene,” Fonda says. By then, the motorcycles had been stolen from a Simi Valley garage where they were stored.

Casting was also done on the fly. The two Southern hunters in the pickup in the violent climax were nonactors who had pulled over out of curiosity in Louisiana to watch the film crew set up. And the rednecks and teenage girls in the tension-filled diner scene were locals (that's a real deputy sheriff, too) who happened to be at the backwater Louisiana cafe.

In that scene, the men hurl insults at Hopper, Fonda and Nicholson and mock the bikers' long hair. To get the newfound extras riled up, Fonda says they were told that in the movie, the trio had just raped and killed a white girl outside of town – which wasn't true. “They became incensed. We said, 'The worst thing you can say about us is perfect.' ”

The cameos are also a trip – the hippies at a commune include Fonda's first wife, Susan Brewer, their children, Bridget and Justin, and Dan Haggerty of “Grizzly Adams” fame. And record producer Phil Spector, now in prison for murdering an actress at his mansion, has a cameo as a cocaine dealer who snorts a sample of his buy. His character arrives in a Rolls with a bodyguard at a runway at Los Angeles International Airport.

“Phil had been a friend and he had his own Rolls-Royce and a bodyguard. It was a budget decision,” Fonda says with a laugh. “Phil was so scared of the planes – he really was ducking.”

The cocaine, which Fonda also tries on-camera, was fake. “That was powdered sugar. Man, that really hurt going up my nose.” And the LSD dropped in the New Orleans segment was actually aspirin.

But Fonda says he provided about a kilo of marijuana that was used whenever the actors smoked weed on-screen. “It was what hippies were doing in those days. And bikers.”

Fonda says he got the idea for his anti-establishment film in 1967, while in Toronto promoting “The Trip,” an LSD-themed movie written by Nicholson and co-starring him, Fonda and Bruce Dern. As he autographed photos, he came across a silhouetted publicity still of himself and Dern riding motorcycles on Venice Beach. It was from their 1966 outlaw biker movie, “The Wild Angels.”

In his new movie, he envisioned “two guys riding across John Ford's West” to retire. In “Easy Rider,” the biker buddies plan to use the coke proceeds, which are stuffed in Captain America's stars-and-stripes gas tank, to retire in Florida.

Looking back, “Easy Rider” made an indelible mark – a 40th-anniversary Blu-ray version comes out in the fall – because “it spoke to this country and it also spoke to an audience which had never had a film made for them,” Fonda says. “The studios were making 'Pillow Talk' with Rock Hudson and Doris Day. We were trying to put out the message of bigotry, injustice, racism. We wanted to show a different part of America.”

And no surprise, Fonda has been repeatedly asked to explain what he meant when he uttered the movie's lingering line, “We blew it.” (He also notes he and Hopper had a screaming fight over the line, but he won.)

“Well, look out the window today,” Fonda muses. “The air is bad, everything has gone further south; it's all gone to hell in a handbasket. We all had this idea you get rich and you're free. And that's wrong.”